Process steam heaters

ABSTRACT

This invention relates to process stream heaters. These heaters comprise a furnace chamber through which a number of tubes carrying the process stream to be heated pass. These tubes must be free to expand along their length but should not distort away from position since such distortion might result in uneven and insufficient heating. According to the invention this distortion is prevented where there are adjacent pairs of rows of tubes by means of a tube guide system comprising a zig-zag lattice made up of a number of clamping bars. Adjacent bars are pivoted to one another near their ends and the tubes nest in and are trapped in the V-shaped openings of the zig-zag lattice. In this way, the tubes are left free to expand and more relatively to one another along their lengths but any attempted distortion of a tube away from its axial position tends to cause pivoting of the clamping bars retaining that tube in place so that the lattice tends to lock more tightly onto other tubes so restraining that tube attempting to distort.

waited States atet [451 Aug. 29, 1972 Holt [54] PROCESS STEAM HEATERS[72] Inventor: Kenneth Holt, Twyford, England [73] Assignee: FosterWheeler Corporation, Livingston, NJ.

[22] Filed: May 5, 1971 [21] Appl. No.: 140,409

[52] US. Cl ..122/356, 122/510 [51] Int. Cl ..F22b 37/24 [58] Field ofSearch ..122/240 R, 356, 510

[56] References Cited UNITED STATES PATENTS 3,026,858 3/ 1962 Fleischer..122/510 3,127,876 4/1964 Olson ..122/356 X 3,240,204 3/1966 Wiesenthal..122/240 3,384,053 5/1968 Fleischer ..l22/5l0 Primary Examiner-KennethW. Sprague Attomey-John Maier, III, Marvin A. Naigur and John E. Wilson[57 ABSTRACT This invention relates to process stream heaters. Theseheaters comprise a furnace chamber through which a number of tubescarrying the process stream to be heated pass. These tubes must be freeto expand along their length but should not distort away from positionsince such distortion might result in uneven and insufficient heating.According to the invention this distortion is prevented where there areadjacent pairs of rows of tubes by means of a tube guide systemcomprising a zig-zag lattice made up of a number of clamping bars.Adjacent bars are pivoted to one another near their ends and the tubesnest in and are trapped in the V-shaped openings of the zig-zag lattice.In this way, the tubes are left free to expand and more relatively toone another along their lengths but any attempted distortion of a tubeaway from its axial position tends to cause pivoting of the clampingbars retaining that tube in place so that the lattice tends to lock moretightly onto other tubes so restraining that tube attempting to distort.

9 Claims, 5 Drawing Figures PATENTEDwszs 1912 SHEET 3 [IF 3 PROCESSSTEAM HEATERS This invention relates to process stream heaters which areused to heat various processing feed streams in a processing plant suchas an oil refinery.

BACKGROUND TO THE INVENTION These heaters generally comprise a furnacechamber provided with one or more burners and through this chamberextend a number of tubes carrying the stream to be heated.

The mounting of these tubes is not simple because one must allow forthem to expand along their length. On the other hand they should retaintheir positions relatively to one another so as to ensure even andsufficient heating. The restraining of the tubes in this way is mademore difficult by the fact that uneven coking may occur in them andaccordingly they may bend from their designed position; Additionally oneor more of the burners in the heater might fail so subjecting differenttubes to different heating effects.

Since the tubes are of quite large diameter, e. g. 8 inches, any attemptto restrain them in place will involve extremely large forces. Thus, oneway of restraining them would be to link them to the walls of theheater. The-great disadvantage of doing this, however, is that the wallswould then need to be of massive construction to resist the forceslikely to be placed in them by the tubes and this solution would,therefore, entail a considerable increase in the cost of the heater andalso in the time and complexity of its construction.

It is, therefore, an object of the invention to provide a relativelysimple way of restraining the tubes relatively to one another in suchheaters.

THE INVENTION According to the invention there is provided a tube guidesystem for a pair of rows of tubes in a heater, the system comprising anumber of clamping bars, pairs of which are pivoted to one another atpositions near their ends so as to form a roughly zig-zag lattice withthe tubes nesting in the troughs defined between crests of the zig-zaglattice, the size of the openings of the troughs between the ends ofclamping bars being less than the diameter of the tubes so that thelatter are trapped in place, whereby the tubes are free to expandrelatively to one another along their lengths but any attempteddistortion of a tube away from its axial position tends to causepivoting of the clamping bars retaining that tube in place so that thelattic tends to lock more tightly onto other tubes and so restrains thetube attempting to distort.

Such a tube guide system is very simple and cheap to install and reliesupon the strength of other tubes to prevent a particular tube fromdistorting. Therefore no special reinforcing of the walls of the heaterare required. When there are a relatively large number of tubes in therows, the system can rely entirely upon the tubes themselves to restrainone another, but when there are relatively few tubes it is oftendesirable to link the ends of the tube support system to opposed wallsof the heater for additional support to the tubes. The force placed onthe end walls is quite small, however, and so they need very little ifany reinforcement.

Although the tube guide system of the invention is very eifective inpreventing distortion of an particular tubes or a number of tubes, awayfrom their axis, it

leaves the tube free for thermal expansion and contraction independentlyof one another along their lengths.

To hold the tubes at the ends of the rows in place, end clamping membersare required which extend sufficiently around the last tubes andco-operate with the clamping members to lock them in position and whichare pivoted to the last clamping bar. When the tube guide system is tobe linked to the walls of the heater, these end clamping members arelinked to the wall.

The tubes in the pairs of rows of tube will normally be spaced andarranged so that their longitudinal axis lay on a triangular pitcharrangement since this ensures a fairly uniform heating of each tuberight the way round its circumference. The invention is equally applicable, however, to the case when the tubes are pitched on a squarepattern or any other pattern.

In order to support the tube guide support system, the clamping bars ofthe system should rest on support members fixed to the outside of thetubes so as to retain the system roughly horizontal.

The tube guide system of the invention is particularly useful in heaterswhere there are four upright sets of tubes through the furnace heatingchamber, these tubes all being formed by bending one length of tubes,two lengths of tubes or all being separate lengths of tubes. The fourupright sets of tubes can be positioned so that a set extends up nearopposite side walls while the remaining two sets extend up side by sidein the middle of the chamber between the side walls. The tube guidesystem is then eminently suitable for restraining the tubes of the twosets extending up the center of the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of a tube support systemaccording to the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a cross-section through a heater employing the system of theinvention;

FIGS. 2 and 3 are enlarged plan views taken in the line A-A of FIG. 1showing the tubes in their normal position and in an exagerated positionshowing attempted distortion of a tube, respectively;

FIG. 4 is an elevational detail in the direction of the line B-B of FIG.2; and

FIG. 5 is a diagrammatic plan view showing the tube arrangement withinthe heater of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The heater 10 shown in thedrawings comprises a furnace heating chamber 12 defined by side walls 14covered with insulation 16 and a floor 18. From the top of the chamberan outlet 20 leads to a stack. In the floor 18 are provided burners (notshown).

Within the chamber 12 are a number of tubes 22 each bent so as to make 4upright passes. The tubes 22 have upright passes 24 and 26 adjacent sidewall 14, two central passes 28 and 30 in the middle of the chamber andthe passes 24 and 28, and 26 and 30 respectively, are joined at theirtops by horizontal passes 32 and 34, while the passes 28 and 30 arejoined at their lower ends by a U bend 36. As shown best in FIG. 4 thepasses 24 and 28, and 26 and 30 are staggered relatively to one anotherso that the tubes in the central passes 28 and 3b are spaced on atriangular pitching.

The tubes 22 are supported by a cross bar 40 in the floor 18 on whichthe bends 36 rest and are restrained by pegs d2 projecting from thetubes into the bar 40 and at the lower ends of the passes 24 and 26.

it is important to restrain the central passes 28 and 30 both relativelyto one another so as to maintain substantially uniform even heating andin their central positions so that unduely large forces are not appliedto the side walls 14. If they are so restrained then the upper ends ofthe passes 24 and 26 need only simply I sliding guides 50 allowingupward thermal expansion and contraction of the tubes of the passes 24and 26 and no large forces will be applied to the side walls ld.

The tube guide system 60 of the invention provides this effectiverestraint upon the tubes of the central passes 28 and 3t) and the systemis shown in more detail in FIG. 2.

The system comprises a number of clamping bars 62, pairs of which arepivoted to one another near their ends by pivot pins 64 (FIG. 3). Nutsand bolts can be used instead of the pins 64. The clamping bars 62 arethus assembled into a horizontal zig-zag configuration and the tubes ofthe passes 28 and 30 are nested in the troughs formed by the zig-zagconfiguration. The distance between the ends of the clamping bars 62defining a trough, i.e., the distance x, is less than the diameter ofthe tubes so that the latter are trapped in the troughs.

The tubes of the passes 28 and 30 have small supports 66 welded to theircircumference and the clamping bars 62 simply rest on these.

At the ends of the system, end clamping members 68 are provided. As canbe seen they are shaped so as to encompass sufficient of each end tubeto trap it in place. The members 68 are pivoted to the final clampingbar 62.

Normally the system 60 will maintain the tubes of the passes 28 and 39in their correct position on its own, but if relatively few tubes arepresent it may be desirable to link the end member 68 through pivotedlinks 70 to front and rear walls 72.

The system 60 restrains the tubes in the following way as will bedescribed in connection with FIGS. 2 and 3. if one of the tubes 128tries to bend away from the upright position through uneven heatingbecause a burner (not shown) has failed or because of coking in thetube, it will try to move in the direction of the arrow 1%. When thishappens, because it is trapped in the trough formed by the bars 62, itattempts to pivot the bars 162 which encircle it in the direction of thearrows 132. in attempting to pivot relatively to one another, the bars162 by a kind of scissors effect grip all the more tightly on the tubesnear to the defecting tube 128. Therefore, to distort, the tube 12% itmust at the same time bend all of the tubes in the pass 30 and althoughsome slight deflection will occur it will be sufficiently small to beunimportant.

it will therefore be realized that, although the system 64) is verysimple and cheap, it is extremely effective in restraining the tubes ofthe passes 28 and 39 in place. In addition it puts very little, if any,additional forces on the walls id and 72 of the heater and so thesewalls do not need costly strengthening.

Although the system gives very effective restraint in the horizontalsense, it leaves the tubes in the passes 28 and 34), plenty of freedomfor thermal expansion and contraction even if adjacent tubes expanddifferently because of say difierent coking within the tubes or if aburner fails and different tubes then expand lengthwise by varyingamounts.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the invention herein.

I claim:

1. A process stream heater comprising a furnace heating chamber, atleast a pair of rows of parallel tubes, said rows extending side by sideacross said chamber, said pair of rows of tubes being restrained bymeans of a tube guide system comprising:

a. a number of clamping bars,

b. pivot means being provided between adjacent pairs of said bars, saidpivot means being provided near ends of said bars leaving free endsprojecting beyond said pivot means, whereby said adjacent clamping barsare pivoted to one another,

c. adjacent pairs of said bars defining V-shaped openings so that saidclamping bars constitute a roughly zig-zag lattice,

d. said tubes of said rows nesting in said V-shaped openings and beingtrapped in said openings by free ends of damping bars,

whereby said tubes are free to expand and move relative to one anotheralong their lengths but any attempted distortion of a tube away from itsaxial posi' tion tends to cause pivoting of said clamping bars retainingthat tube in place so that said lattice tends to lock more tightly ontoother tubes so restraining that tube attempting to distort.

2. A process stream heater according to Claim 1 further comprising atsaid ends of said lattice end clamping members, means for pivoting saidend clamping members to said clamping bars at at said end of saidlattice, said end clamping members comprising an arm by means of whichsaid member is pivoted to said adjacent clamping bar, and a pair of lugshaving part circular shaped recesses in which tubes are arranged to nestand be trapped in place.

3. A process stream heater according to claim 2 further comprisingopposed side walls defining said furnace heating chamber and pivot meanspivotally linking said end clamping members to said opposed side walls.

d. A process stream heater according to claim 1 in which said tubes ineach of said pair of rows of tubes stagged relative one another so thattheir longitudinal axis are arranged on a triangular pitch.

5. A process stream heater according to claim 1 further comprisingsupport members fixed to said tubes, said clamping bars resting on saidsupport membets.

6. A process stream heater according to claim 1 comprising opposed sidewalls defining said further heating chamber, an upright substantiallyparallel row of tubes extending rear to each opposed side wall and saidpair of rows of parallel tubes extending side by side across the furnaceheating chamber, said pair of row of tubes being restrained by said tubeguide system.

7. A process stream heater according to claim 6 in which all of saidrows of tubes have been formed by bending lengths of tubes so thatcorresponding tubes in all rows are connected by series flow.

8. In a process stream heater a pair of rows of parallel tubes extendingside by side which are restrained by a tube guide system comprising:

a. a number of clamping bars,

b. pivot means being provided between adjacent pairs of said bars, saidpivot means being provided near ends of said bars leaving free endsprojecting

1. A process stream heater comprising a furnace heating chamber, atleast a pair of rows of parallel tubes, said rows extending side by sideacross said chamber, said pair of rows of tubes being restrained bymeans of a tube guide system comprising: a. a number of clamping bars,b. pivot means being provided between adjacent pairs of said bars, saidpivot means being provided near ends of said bars leaving free endsprojecting beyond said pivot means, whereby said adjacent clamping barsare pivoted to one another, c. adjacent pairs of said bars definingV-shaped openings so that said clamping bars constitute a roughlyzig-zag lattice, d. said tubes of said rows nesting in said V-shapedopenings and being trapped in said openings by free ends of dampingbars, whereby said tubes are free to expand and move relative to oneanother along their lengths but any attempted distortion of a tube awayfrom its axial position tends to cause pivoting of said clamping barsretaining that tube in place so that said lattice tends to lock moretightly onto other tubes so restraining that tube attempting to distort.2. A process stream heater according to Claim 1 further comprising atsaid ends of said lattice end clamping members, means for pivoting saidend clamping members to said clamping bars at at said end of saidlattice, said end clamping members comprising an arm by means of whichsaid member is pivoted to said adjacent clamping bar, and a pair of lugshaving part circular shaped recesses in which tubes are arranged to nestand be trapped in place.
 3. A process stream heater according to claim 2further comprising opposed side walls defining said furnace heatingchamber and pivot means pivotally linking said end clamping members tosaid opposed side walls.
 4. A process stream heater according to claim 1in which said tubes in each of said pair of rows of tubes staggedrelative one another so that their longitudinal axes are arranged on atriangular pitch.
 5. A process stream heater according to claim 1further comprising support members fixed to said tubes, said clampingbars resting on said support members.
 6. A process stream heateraccording to claim 1 comprising opposed side walls defining said furtherheating chamber, an upright substantially parallel row of tubesextending near to each opposed side wall and said pair of rows ofparallel tubes extending side by side across the furnace heatingchamber, said pair of row of tubes being restrained by said tube guidesystem.
 7. A process stream heater according to claim 6 in which all ofsaid rows of tubes have been formed by bending lengths of tubes so thatcorresponding tubes in all rows are connected by series flow.
 8. In aprocess stream heater a pair of rows of parallel tubes extending side byside which are restrained by a tube guide system comprising: a. a numberof clamping bars, b. pivot means being provided between adjacent pairsof said bars, said pivot means being provided near ends of said barsleaving free ends projecting beyond said pivot means, whereby saidadjacent clamping bars are pivoted to one another, c. adjacent pairs ofsaid bars defining V-shaped openings so that said clamping barsconstitute a roughly zig-zag lattice, d. said tubes of said rows nestingin said V-shaped openings and being trapped in said openings by freeends of clamping bars.
 9. In the heater of claim 8 support member fixedto said tubes, said clamping bars resting on said support members.